This invention relates to a method of carrying out the gasification of solid carbonaceous materials such as coal, coke or the like (sometimes referred to as "coal" collectively hereunder) by blowing coal and oxygen together with a supplementary gasifying agent such as steam or carbon dioxide gas onto a high temperature molten metal bath.
In particular, this invention relates to the gasification method defined above, which can achieve improvements in thermal efficiency during gasification, and which can also achieve precise control of the temperature of a molten metal bath and a prolonged service life of the lance used in blowing oxygen and coal.
Generally speaking, so-called coal gasification using a molten metal bath in a gasification furnace is a method wherein the heat necessary for the gasification is supplied from the molten metal. The gasification of coal is effected through reactions between carbon in the molten metal and oxygen gas. The carbon in the molten metal is derived from the coal which is supplied.
The basic idea of coal gasification using a molten metal bath is schematically shown in FIG. 1. A melting furnace, i.e. gasification furnace 1, contains a substantial amount of molten metal, usually molten iron 2. Through a non-immersing lance 3, coal 5, oxygen 6, and a supplementary gasifying agent 7 such as steam, carbon dioxide gas, and mixtures thereof are top-blown onto the molten metal to effect the gasification of coal. See copending U.S. Ser. No. 404,332, now U.S. Pat. No. 4,459,137, and U.S. Pat. Nos. 4,388,084 and 4,389,246. The non-immersing lance may be replaced by an immersing lance or bottom-blowing nozzle (not shown in FIG. 1). See U.S. Pat. Nos. 3,526,478 and 3,533,739, which disclose a gasification furnace provided with a bottom-blowing nozzle. The slag formed on the surface of the molten metal is indicated by reference number 4. The supplementary agent 7 such as steam or carbon dioxide gas serves as a cooling agent to control the temperature of the molten metal bath while coal gasification is being carried out. In case steam or carbon dioxide gas is used, it serves as an additional oxygen source, too. Such a cooling agent is effective for promoting a water gas reaction with carbon in the molten metal or a carbon solution reaction.
It is conventional in the gasification of coal to supply the supplementary gasifying agent separately from the primary gasification agent (i.e., oxygen gas), blowing it through a non-immersing lance, immersed lance, or bottom-blowing nozzle.
In case a non-immersing lance is used, although a prolonged service life of the lance can be attained, the supplementary agent such as steam reacts with CO in the atmosphere before it reacts with carbon in the molten metal on the surface of the bath. (CO+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2).
Alternatively, if a sharpened local cooling is caused by the supplementary agent, the reaction temperature is lowered, resulting in a decrease in the rate of the water gas formation or carbon solution reaction. This means that the supplementary agent, which is also a cooling agent, does not exert its cooling effect to a sufficient degree, nor does it serve as an effective supplementary agent, resulting in less improvement in thermal efficiency during gasification even if such a cooling agent is added.
On the other hand, a method using an immersed lance or bottom-blowing nozzle can improve the rate of a water gas reaction with carbon in the molten metal and it also increases the reaction rate of carbon solution, resulting in an increase in the thermal efficiency. However, such a method is not practical, since the damage of lances or nozzles due to the hot molten metal is marked, making a continuous long-lasting gasification operation impossible.
In a method of coal gasification using a molten metal bath, it is necessary that the supplementary gasifying agent (i.e., the cooling agent) be dissolved and diffused into a molten metal bath in an efficient manner so as to increase the chances of the cooling agent contacting carbon in the molten metal. It is also necessary to place the lance as far as possible from the molten metal bath so as to prolong its service life.
However, in the conventional method, a plurality of lances for coal, oxygen gas and the supplementary agent, respectively, are used, or a multihole lance having a plurality of injection nozzles for coal, oxygen gas, and the supplementary gas, respectively, is used. The oxygen gas and supplementary gas are separately blown onto the molten metal bath, resulting in less efficient dissolving of the supplementary agent in the bath.